1. Field of the Invention
The present invention relates to an improvement in or relating to a drive shifting system for use with an automotive vehicle, and more particularly to an improved drive shifting system for shifting the drive position between two and four wheel drive which is specifically designed to be compact and light weight so that it can be adapted to a light-weight automotive vehicle.
2. Description of the Prior Art
It is generally known that the four-wheel drive system has been extensively employed in automotive vehicles used for specific purposes such as a jeep, a saddle-riding type off-road vehicle, a special service vehicle for carrying heavy loads, a truck for towing a trailer, and the like.
There is shown, in general view and schematic view, a typical four-wheeled light saddle-type vehicle for off-road or irregular field services and a general power line lay-out thereof in FIGS. 4 and 5, respectively.
A typical four-wheel drive system for use with a four-wheeled saddle-type vehicle for irregular field services is designated generally by the reference numeral 100. There is provided a pair of front wheels designated at 101 and a pair of rear wheels at 102, a propeller shaft at 103 and an internal combustion engine at 104, the propeller shaft 103 being adapted to transmit the driving power generated from the engine 104 to the front wheels 101, and connected operatively through a differential gear unit designated at 105 to front drive axles at 106 and 107 which mount rotatably the right and left front wheels, respectively.
Also, FIG. 6 is a general cross-sectional view showing the typical general arrangement of a conventional drive shifting system for shifting the power trains or driving positions from a two-wheel set to a four-wheel set, and vice-versa of a vehicle, which is mounted operatively in the differential gear unit 105, wherein there is shown a small reduction gear 108 to which the driving power from the engine 104 is transmitted by the propeller shaft 103, a large reduction gear 109 mounted on a drive sleeve 110 which is held rotatably by one driving axle 106, and a driving wheel 111 spline-connected upon the driving axle 106, in which a plurality of openings 112 are formed at a predetermined space from each other in the circumference of the plate portion of the driving wheel. There are also provided a plurality of claws or dogs 113 on the other driving axle 107, which are disposed in an opposed operative relationship with the plurality of openings 112 formed in the driving wheel 111. A sliding wheel at 114 is spline-connected upon the drive sleeve 110, and is provided with a plurality of claws or dogs 115 disposed in an opposed operative relationship with the plurality of openings 112 formed in the driving wheel 111.
According to such a typical construction of the conventional two-and-four-wheel drive shifting system as noted above, when the normal two-wheel drive of a vehicle is desired, it is generally arranged that the driving power from the engine 104 is shifted to a drive position for driving the rear axle so that the pair of rear wheels 102 are driven in rotating motion. At the same time, the small reduction gear 108 is driven in rotation from the rotation of the propeller shaft 103 via the transmission means incorporated in the vehicle, thus causing the large reduction gear 109 to be driven in rotation. Then, the large reduction gear 109 is driven to rotate with the drive sleeve 110, which would then cause the sliding wheel 114 to be driven in rotation. At this moment, since the sliding wheel 114 is still disconnected from the driving wheel 111 and the dogs 113, both the left and right front drive axles 106, 107 are free from the driving position so that the front wheels 101 may rotate only because of the tractive motion of the rear wheels 102, thus providing the two-wheel drive of a vehicle, accordingly.
Next, when the four-wheel drive is desired by a driver of the vehicle, it requires a shifting motion of a drive shift lever at the driver's seat, not shown, to the four-wheel drive position so that the sliding wheel 114 may be caused to shift in the axial direction shown by an arrow in FIG. 6 by function of a drive shift fork, not shown. The sliding wheel 114 is then caused to engage operatively with the driving wheel 111 with its dogs 115 inserted into the openings 112 in the wheel 111 to such an extent that these dogs 115 may engage mutually with the driving dogs 113 on the part of the front drive axle 107. With this engagement, when the driving wheel 111 is driven in rotation, the front drive axle 106 may now be rotated together with the other drive axle 107. Now, the pair of front wheels 101 are caused to be driven in rotation with the power transmission from the engine, whereby the saddle-type off-road vehicle 100 can then be put in the four-wheel drive position, accordingly.
In accordance with the typical construction of the two-and-four-wheel drive shifting system of the prior art, the sliding wheel 114 is kept in rotating motion even during the two-wheel driving operation thus, it is inevitable that the sliding wheel 114 may be subjected to possible damages, and also that the entire drive shifting system would tend to be cumbersome because of the relatively long extension of the sliding wheel 114.
On the other hand, there is also provided another type two-and-four wheel drive shifting system wherein there is employed a differential gear unit 116 between the front drive axles 106, 107 of the front wheels 101 as typically shown in FIG. 7, in which there is provided a large reduction gear 118 in a differential gear box 117. With this arrangement, there is provided a small reduction gear 119, which is adapted to drive the large reduction gear 118, and this small reduction gear 119 is connected operatively to a driving shaft 120 by way of a spline coupling 121, with the driving shaft 120 being driven in rotation from the propeller shaft 103. In this system construction, the spline coupling 121 is designed to connect and disconnect the small reduction gear 119 with the driving shaft 120 by the selective sliding motion of a movable spline element 123, which is adapted to move in sliding motion by function of a fork 122 between the engagement positions with splines 124 and 125 provided in the small reduction gear 119 and the driving shaft 120, respectively.
According to such a typical construction in a conventional two-and-four wheel drive shifting system, it is generally arranged that for the two-wheel drive of the vehicle the movement of the fork 122 will cause the movable spline element 123 to disengage from the splines 124 which rotate the small reduction gear 119. With this shifting action, both the left and right front wheels 101 are put into a coupling arrangement with each other through the differential gear unit 116 for the normal running operation of the vehicle.
Next, when the four-wheel drive of the vehicle is desired, the fork 122 is actuated so as to have the movable spline element 123 shifted in the longitudinal direction, thereby causing both the splines 124, 125 to be engaged with each other through the spline element 123. With this operation, it is seen that the driving power on the propeller shaft 103 is transmitted to the small reduction gear 119 through the driving shaft 120, then to the splines 125, an to the movable spline element 123 and then to the splines 124, thus having the differential gear box 117 driven in rotation by the rotating motion of the large reduction gear 118, and thus causing the both driving axles 106, 107 to be rotated through the planetary gears in the differential gear unit 116, accordingly.
In this type of four-wheel drive system, when it is required to have the differential gear unit 116 locked in its operative motion for attaining the effect of rigid axle, it is generally the practice to provide in addition a lock mechanism as typically shown in FIG. 6, which would result in a relatively large sized and complex construction of the entire drive shifting system.
In consideration of the drawbacks in the conventional construction of a two-and-four wheel drive shifting system as noted above, it would be desirable to attain an efficient resolution of the problems present in the conventional construction.
The present invention is essentially directed to the provision of a resolution of the problems as outlined above and experienced in the conventional two-and-four wheel drive shifting system which have not been properly solved.